Specifications

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Cisco ONS 15530 Planning Guide
OL-7708-01
Chapter 5 Amplified Network Planning
Amplified Network Planning Considerations
You can use WB-VOA modules for the following types of attenuation:
• Per channel—attenuate only a single data channel or the OSC. Place the WB-VOA module between
the line card and the OADM.
• Wide band—attenuate all channels on the trunk signal. Use this configuration to avoid saturating the
amplifiers.
• Pass through band channels—attenuate the pass through bands by an OADM. Place the WB-VOA
on the upgrade, or thru, output port on the OADM.
Amplified Network Planning Considerations
When planning an amplified network topology, you need to consider the following:
• Optical power budget
• OSNR (optical signal-to-noise ratio)
• Chromatic dispersion
Optical Power Budget
Optical power budgets, or link loss budgets, are a critical part of planning an optical network. In general,
there are many factors that can result in optical signal loss. The most obvious of these is the distance of
the fiber itself. Also, the number of nodes in a network topology is a significant contributor to optical
loss.
The key to precise optical power budget calculation is to get an accurate reading on the fiber using an
optical time domain reflectometer (OTDR). Using an OTDR, you can obtain the following information
about a span:
• Length of the fiber
• Attenuation of the whole link, as well as the attenuation of separate sections of the fiber (if any)
• Attenuation characteristics of the fiber itself
• Locations of connectors, joints, and faults in the cable
The goal in calculating optical loss is to ensure that the total loss does not exceed the span budget. The
following are typical values for the main elements in a span:
• Connector splice loss
• Fiber loss
• Fiber aging
It is also important to ensure that the client side or tributary equipment does not overload the local
receive laser of the DWDM equipment. This means that the client or tributary equipment must operate
within the specifications of the DWDM client interface.
OSNR
Besides the signal itself, optical amplifiers boost the entire input, including noise. The effect is
cumulative through the network. The OSNR (optical signal-to-noise ratio) can become so low that a clear
signal is not correctly decoded at the receiving end. At this point the signal must be regenerated.